Well turned out to be 3in chambers, massive big heavy thing with a push forward under lever, hammerless, 10 Bore + size, cocking indicators, cut file rib, no sights & no rifling !

So I'm thinking a very heavy Wild Fowl gun or Ball Gun, but no sights ?

I did not bring it home, he had a 8 bore ML shotgun to but I ran out of money for that one.